Heat dissipating device with preselected designed interface for thermal interface materials

ABSTRACT

Embodiments of the invention includes a heat dissipating device. The heat dissipating device includes a main body having a surface, wherein the surface is plated or coated with at least two different metals to form a design effective for bonding to solder and for adhering to polymer in a polymer solder hybrid. The heat dissipating device also includes surface perturbations.

TECHNICAL FIELD OF THE INVENTION

Embodiments of the invention relate generally to integrated circuitpackages. More particularly, embodiments of the invention relate tomethods and devices for improving reliability performance of thermalinterface materials employed in integrated circuit packages.

BACKGROUND OF THE INVENTION

In the field of electronic systems there is an incessant competitivepressure among manufacturers to drive the performance of their equipmentup while driving production costs down. This is particularly trueregarding the packaging of integrated circuits, IC's, on substrates,where each new generation of packaging must provide increasedperformance, particularly in terms of an increased number of componentsand higher clock frequencies, while generally being smaller or morecompact in size. As the density and clock frequency of IC's increase,the IC's accordingly generate a greater amount of heat. However, theperformance and reliability of IC's are known to diminish as thetemperature to which they are subjected increases, so it becomesincreasingly important to adequately dissipate heat from ICenvironments, including IC packages.

An IC substrate typically comprises a number of metal layers selectivelypatterned to provide metal interconnect lines (referred to herein as“traces”), and one or more electronic components mounted on one or moresurfaces of the substrate. The electronic component or components arefunctionally connected to other elements of an electronic system througha hierarchy of electrically conductive paths that include the substratetraces. The substrate traces typically carry signals that aretransmitted between the electronic components, such as IC's, of thesystem. Some IC's have a relatively large number of input/output (I/O)terminals (also called “lands”), as well as a large number of power andground terminals or lands.

As the internal circuitry of IC's, such as processors, operates athigher and higher clock frequencies, and as IC's operate at higher andhigher power levels, the amount of heat generated by such IC's canincrease their operating temperature to unacceptable levels.

Heat spreaders are employed to dissipate the heat generated. A heatspreader is usually located above the die and is thermally coupled tothe die by a thermal interface material.

For the reasons stated above, and for other reasons stated below whichwill become apparent to those skilled in the art upon reading andunderstanding the present specification, there is a significant need inthe art for apparatus and methods for packaging an IC on a substratethat minimize heat dissipation problems associated with high clockfrequencies and high power densities.

DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a top plan view of a checkered grid design of theheat dissipation device embodiment of the invention.

FIG. 2 illustrates a top plan view of a circle pattern grid design ofthe heat dissipation device embodiment of the invention.

FIG. 3 illustrates a top plan view of a bull's eye pattern of the heatdissipation device embodiment of the invention.

FIG. 4 illustrates a top plan view of a pattern of the heat dissipationdevice embodiment of the invention.

FIG. 5 illustrates a side view of a microelectronic package thatincludes the heat dissipation device embodiment of the invention.

FIG. 6 illustrates a perspective view of the heat dissipation deviceembodiment of the invention.

FIG. 7 illustrates a cross-sectional view of serrations in an integratedheat spreader device embodiment of the invention

FIG. 8 illustrates a prior art interface between a thermal interfacematerial and a heat transfer device surface.

FIG. 9A illustrates schematically, an integrated heat spreader with acrack arrester.

FIG. 9B illustrates schematically, a prior art integrated heat spreaderfree of a crack arrester.

FIG. 10 illustrates a cross-sectional view of a multi-die assembly thatincludes a heat dissipation device embodiment of the invention withelectronic devices positioned side-by-side.

FIG. 11 illustrates a cross-sectional view of a multi-die assembly thatincludes a heat dissipation device embodiment of the invention withstacked electronic devices.

FIG. 12 illustrates a cross-sectional view of a die assembly thatincludes a metal substrate stiffener and a heat dissipation deviceembodiment of the invention.

FIG. 13 illustrates a schematic view of a fan, including its tangentialand axial air flow components, and a side view of a bent fin heat sinkas positioned upon a sectioned integrated circuit (IC) package on asubstrate, in accordance with one embodiment of the invention.

DETAILED DESCRIPTION

One embodiment of the invention includes a heat dissipating device. Theheat dissipating device includes a main body having a surface that isplated or coated with at least two different metals to form apreselected design effective for bonding to solder and for adhering topolymer. When the heat dissipating device surface comprising twodifferent materials in a preselected design is contacted to a polymersolder hybrid (PSH) thermal interface material (TIM), the contactimproves the bonding and adherence of the polymer solder hybrid to theheat dissipating device and prevents delamination of the polymer solderhybrid thermal interface material.

In a second heat dissipating device embodiment, surface perturbations,such as serrations, grooves and channels are made in the surface orsurfaces of the heat dissipating device that are capable of contactingthermal interface material. The surface perturbations act to enhanceadhesion and to prevent delamination between the TIM and the heatdissipating device.

One other heat dissipating device embodiment of the invention includesboth of the surface features of the preselected design and one or moresurface perturbations. For some embodiments, surface perturbations suchas serrations, channels or grooves or combinations of serrations,channels and grooves are added to the surface in accordance with thepreselected pattern of metal plating. For other embodiments, the surfaceperturbations are randomized. That is, for some embodiments, theperturbations form a grid or a bull's eye and for other embodiments, theperturbations are randomized. For other embodiments, the surfaceperturbations are positioned on a surface or surfaces that are differentfrom the surface or surfaces treated with the preselected two metaldesign.

Another embodiment of the invention further includes an integratedcircuit package that includes one or more of the heat dissipating deviceembodiments of the invention, an electronic system that includes one ormore of the heat dissipating device and methods for making these devicesand systems.

Delamination in polymer solder hybrid thermal interface materialscontacting integrated heat spreader surfaces is a root cause for thermalinterface material failure in some types of microelectronic packages.Typical nickel plated integrated heat spreaders offer good adhesion andwettability to the polymer component of the polymer solder hybrid (PSH).However, the solder component does not bond or wet the nickel heatspreader surface effectively to withstand thermomechanical stressesexperienced in package reliability tests. Gold and silver plated nickelsurfaces display good adhesion and wettability to the solder componentof the polymer solder hybrid. However, the polymer adhesion to gold andsilver is weak and fails in reliability tests.

To optimize and bridge the dual polymer solder hybrid componentrequirements, embodiment of the invention include a method for platingtwo metals in a pattern or design, wherein one metal is conducive tobinding with the solder and the other metal is conducive to polymeradhesion. The duality improves the overall adhesion and bonding of thepolymer solder hybrid thermal interface material to the heat dissipatingdevice.

By preventing delamination, integrated circuits, electronic assembliesand electronic systems employing embodiments of the invention are betterable to withstand warpage induced stresses and to maintain interfacialcontact because the heat dissipating device embodiments of the inventionhave a resistance to thermomechanical stresses on the thermal interfacematerials (TIMs). Maintaining contact through bonding and adhesionbetween the polymer solder hybrid thermal interface material andintegral heat spreader reduces the interfacial contact resistance andprevents thermal performance degradation.

As used herein, heat dissipating devices include but are not limited todevices such as integrated heat spreaders, heat sinks, heat fins, fans,vapor chambers and other heat removal devices. The main body of the heatdissipating device is fabricated using materials that include metalssuch as gold, nickel, and copper, composite materials, diamond, AlSiC,and other heat conductive materials capable of being plated.

Polymer solder hybrid (PSH) as used herein refers to an interpenetratingpolymer/metal network formed in situ from a conductive particle andpolymer blend. The polymer/metal network forms simultaneously with thecure of the polymer by a process known as transient liquid phasesintering (TLPS). Conductive particles in a polymer solder hybridinclude metal powders and solder powders. Metal powders include copperpowder, silver powder, aluminum powder, gold powder, platinum powder,palladium powder, beryllium powder, rhodium powder, nickel powder,cobalt powder, iron powder, molybdenum powder, as well as high-meltingpoint alloys of any two or more of these metals, may be employed. Solderpowders include Sn, Bi, Pb, Cd, Zn, Ga, In, Te, Hg, Tl, Sb, Se, Po, ormixtures of any two or more thereof, or another metal or alloy having amelting point lower than that of the metal powder in component.Polymeric resins usable in the polymer solder hybrid include anythermosetting resin (either monomeric or polymeric) that iscross-linkable by the curing agent, a metal catalyst or a hydroxylgroup-bearing agent. Resins which meet this requirement include epoxies,phenolics, novalacs (both phenolic and cresolic), polyurethanes,polyimides, bismaleimides, maleimides, cyanate esters, polyvinylalcohols, polyesters, polyureas, acrylics, polyarnides, polyacrylates,polysiloxanes, cyanoacrylates, and the like. Other resin systems aremodifiable to be cross-linkable by the curing agent, a metal catalyst ora hydroxyl group-bearing agent. Examples of such resins includeacrylics, rubbers (butyl, nitrile, etc), polyamides, polyacrylates,polyethers, polysulfones, polyethylenes, polypropylenes, polysiloxanes,polyvinyl acetates/polyvinyl esters, polyolefins, cyanoacrylates,polystyrenes, and the like.

The heat dissipating device embodiments of the invention improve bondingand adherence of the polymer solder hybrid by employing metals thatenhance both bonding to the metal and solder particles and adherence topolymeric components in the polymer solder hybrid. In one embodiment, apreselected pattern is formed by coating or plating a heat dissipatingdevice surface with nickel and then overlaying portions of the nickelwith gold to form the pattern. The gold bonds with the metal or solderin the polymer solder hybrid. The nickel adheres to the polymer in thepolymer solder hybrid. As a result, both phases of the polymer solderhybrid have a compatible, effective, bonding or adhering surface.

Other metal combinations suitable for use in embodiments of theinvention include nickel/silver, copper/gold, copper/silver,copper/nickel and other metal combinations wherein one of the metalsimproves bonding to solder and metal and the other metal improvesadhesive affinity to polymer in a polymer solder hybrid. Preselecteddesigns usable in the heat dissipating device embodiments of theinvention include a checkered grid, one embodiment of which isillustrated at 10 in FIG. 1. Other pattern embodiments of the inventioninclude a fine or a coarse square grid, a fine or coarse circle pattern,wherein the fine circle grid is illustrated at 20 in FIG. 2, a fine or acoarse bull's eye pattern, wherein the coarse bull's eye pattern isshown at 30 in FIG. 3, a pattern such as is illustrated at 40 in FIG. 4and other patterns that improve bonding and adherence. Other patternsinclude but are not limited to crossing lines, and dot patterns.

Polymer adhesion to metals improves with mechanical interlocking. Theadhesion between thermal interface materials and heat dissipationdevices in microelectronic packages is enhanced by making perturbationssuch as grooves and channels into the integrated heat spreader cavitysurface as shown in FIG. 7. A serrated heat spreader surface embodimentof the invention, shown at 72 in FIG. 7, provides mechanical interlocksfor solder columnar structures for locking into the thermal interfacematerial integrated heat spreader interface 73, thereby improving theinterfacial adhesion and bonding.

In one embodiment, the design patterns provide additional surface areafor bonding as well as mechanically anchoring the polymer to theintegrated heat spreader surface. This mechanical interlocking improvesintrinsic adhesion forces. Mechanical interlocking also arrests crackpropagation due to the discontinuous interfacial pathways formed by thegrooves and channels. The grooves and channels play a role incontrolling interfacial delamination at the thermal interface materialintegral heat spreader interface. It is believed that any delaminationcrack although initiated, is trapped and stopped from growing further,by the surface perturbations, thereby controlling polymer-metal adhesionfailure.

One prior art polymer solder hybrid thermal interface material is shownin cross-section at 80 in FIG. 8. The processes of curing and reflowform predominantly solder columnar structures 82 that physically wet aflat integral heat spreader surface 84. The solder columns are notmechanically bonded to the integral heat spreader surface, however. As aresult, the thermal interface material is susceptible to delamination.

In the absence of the serrations and channels of embodiments of theinvention, a crack generated in the thermal interface material continuesunchallenged, as shown in a prior art thermal interface material crosssection in FIG. 9A. With an integrated heat spreader embodiment of theinvention, a crack propagation in the thermal interface material turnsperpendicular and is arrested, as shown in FIG. 9B.

In another perturbed surface embodiment, a pre-attached solder isapplied to a serrated cavity. The pre-attached solder is applied by coldforming or by solder intermetallic compound (IMC) formations. A heatdissipating device that includes this embodiment is usable with avariety of thermal interface material technologies including polymer,polymer solder hybrid and other types of thermal interface materials.The perturbed surface embodiments that include the serrated, channeledor grooved integral heat dissipating device embodiments of the inventionare also usable with a variety of thermal interface materialtechnologies including polymer, polymer solder hybrid and other types ofthermal interface materials.

In one invention embodiment, the heat dissipating device is a component52 of a microelectronic package, such as is shown at 50 in FIG. 5. Themicroelectronic package also includes a package substrate 12, a die 14,a preform 16, and polymer solder hybrid material 20. The heatdissipating device 52 includes legs 54 and 56 that contact the packagesubstrate 12. Each of the legs 54 and 56 has a surface, 58 and 59,respectively, that contacts the polymer solder hybrid material 20. Thesesurfaces, 58 and 59, have the preselected design that both adheres andbonds the heat dissipating device 52 to the package substrate. The heatdissipating device 52 also includes surface 36 that opposes the preform16. A layer of polymer solder hybrid thermal interface material 20contacts the preform 16 and the heat dissipating surface 36. The heatdissipating device surface 36 also includes one of the preselecteddesign embodiments of the invention, other embodiments of which areshown in FIGS. 1-4.

While a heat dissipating device is shown having the preselected designon surfaces 58, 59, and 36, it is understood that other embodimentsinclude the preselected design on one or more other surfaces contactinga polymer solder hybrid thermal interface material.

Further, the preselected design on surface 36 is, for some embodiments,the same as the preselected design on surfaces 58 and 59. For otherembodiments, the preselected designs on separate surfaces are different.In other embodiments, the heat dissipating device has one single designthat extends over the heat dissipating device surface.

Additional embodiments further include perturbations defined by one ormore of surfaces 36, 58 and 59. The perturbations include serrations andchannels. In other embodiments, the perturbations include pre-attachedsolder.

One exemplary heat dissipating device 62 invention embodiment, isillustrated in FIG. 6. The device 62 is made of a highly thermallyconductive material. The shape of the device 62 is obtained in astamping operation. The device 62 includes a central heat spreaderportion 64 and four bottom surfaces 66A, 66B, 66C and 66D. Each bottomsurface 66A-D extends from a respective edge of the heat spreader 64.

The heat spreader device 62 includes a square region 40 and a centralface 36 wherein the central face 36 is located in a lower plane than theregion 40. Inclined faces 38A-D form walls between the square plane 40and the central face 36.

The patterned metal plating is applied, in one embodiment, on thesurface of the central face 36 that is positioned to oppose a preform,such as is shown at 16 in FIG. 5. The patterned metal plating is alsoapplied to surfaces of 66A, 66B, 66C, and 66D that contact polymersolder hybrid TIM. In the embodiment shown, a circle grid is applied tothe surfaces 66A-D. A bull's eye design is applied to surface 36.Channels are formed around the circles in the grid design. Serrationsare formed around the bull's eye in the surface 36.

One method of application includes use of a fine mask for patternedplating. The patterned metal plating is usable on with any type of heatdissipating device capable of being plated.

In another heat dissipating device embodiment, illustrated at 70 inFIG.7, the device 70 includes a surface that defines one or more ofgrooves, channels, serrations or other features capable of functioningas mechanical interlocks. The interlocks mechanically interlock atemperature interstitial material to the heat dissipating devicesurface. The interlocks improve adhesion between the heat dissipatingdevice surface 72 and the TIM 74. Additionally, the grooves, channels,and serrations arrest delamination crack propagation. In particular, thegrooves, channels and serrations increase the surface area available forbonding and mechanical interlocking with the TIM and improve interfacialadhesion and robustness.

In making a package employing the heat dissipating device 70, the soldercomponent of the thermal interface material flows completely over theserrated integrated heat transfer surface. The reflowed solder thermalinterface material bonds to the solder component in the polymer solderhybrid thermal interface material serrated integrated heat spreadersurface, forming continuous pathways between the integrated heatspreader and the die interfaces. The improved TIM-integrated heatspreader surface adhesion reduces contact resistance at the interfaceand improves thermal performance of the package.

Integrated circuits (IC's) that employ the heat dissipating deviceembodiments of the invention are typically assembled into packages byphysically and electrically coupling them to a substrate made of organicor ceramic material. One or more IC packages are physically andelectrically coupled to a printed circuit board (PCB) to form an“electronic assembly”.

A multi-die assembly embodiment 100 of the invention is shown in FIG.10. The assembly 100 includes a package 120. Extending from the package120 are a plurality of pins 140 that are soldered to an external printedcircuit board 160. The printed circuit board 160 optionally includesother integrated circuit packages that are also mounted to the board 160which communicate with the devices within the assembly 100. The package120 is constructed from materials that include molded plastic, co-firedceramic or any other suitable electronic packaging material. The package120 contains internal routing, which is not shown, to provide power andsignals to the devices within the assembly 100. Although a plurality ofpins 140 are shown and described, it is to be understood that theassembly 100 includes a plurality of solder pads that are soldered tothe printed circuit board 160.

Mounted to the package 120 are a first electronic device 180 and asecond electronic device 200. The electronic devices include any passiveor active electrical device. By way of example, the first device 180 isa microprocessor and the second device 200 is a second level cachememory chip. The devices 180 and 200 are electrically interconnectedwithin the assembly 100. The electronic devices 180 and 200 areconnected by a tape automated bonding (TAB) tape 220 that is attached tocorresponding bonding pads 230 of the devices and the package 120. Thebonding pads 230 are connected to the pins 140 by internal routing ofthe package 120. The TAB tape 220 has routing that allows the firstelectronic device 180 to access the second electronic device 200 withouthaving to route signals through the package 120 and external circuitboard 160, thereby improving the speed and performance of the system.Although only two electronic devices are shown and described, it is tobe understood that the assembly 100 optionally includes additionaldevices.

The electronic devices 180 and 200 both generate heat. In oneembodiment, one device generates more heat than the other device so thatthe operating temperatures of the devices are different. For example,the first electronic device 180 generates more heat, and thus operatesat a higher temperature, than the second electronic device 200.

A heat spreader 240 is coupled to both electronic devices 180 and 200 tomore evenly spread the heat and create a relatively uniform temperatureprofile for the two devices. The heat spreader 240 allows heat to flowfrom one device to the other device, so that both devices operate atapproximately the same temperature. The heat spreader 240 provides aheat sink, which has a base temperature that is common for both devices.The heat spreader 240 is preferably constructed from copper, aluminum orsome other thermally conductive material. In one embodiment, the package120 contains a plurality of thermal vias that provide a direct thermalpath from the devices to the heat spreader 240.

The heat spreader 240 is mounted to the package with a thermal interfacematerial 260. The surfaces 290 and 291 of the heat spreader 240 thatcontact the thermal interface material 260 are each patterned with aplated or coated design, such as is shown in FIGS. 1, 2 and 3. In oneembodiment, the surfaces 290 and 291 of the heat spreader 240 alsoinclude perturbations, such as channels, serrations, and grooves. Inanother embodiment, the surfaces 290 and 291 of the heat spreaderinclude perturbations but are not plated or coated. In anotherembodiment, one of the heat spreader surfaces 290 is coated or platedwith a pattern such as is shown in FIG. 1, 2, or 3 or other preselecteddesign. The other heat spreader surface 291 includes perturbations,channels or serrations. In another embodiment, the heat spreader surface291 has a different design pattern from the heat spreader surface 290.

To reduce the thermal resistance of the assembly 100, a heat slug 280 isattached to the heat spreader 240. The heat slug 280 is constructed froma thermally conductive material such as copper or aluminum. The heatslug 280 is attached to the heat spreader 240 by thermal interfacematerial 250 at surface 281. The surface 281 is, in one embodiment, alsocoated or plated to form a pattern such as is shown in FIG. 1, 2 or 3 orother preselected design. In another embodiment, the surface 281includes perturbations.

The heat slug 280 includes a top that is typically exposed to theambient and provides a heat transfer surface between the assembly 100and the surrounding air. The heat spreader 240 and slug 280 are, forsome embodiments, embedded in a plastic package or bonded to a ceramicpackage. The package includes a lid 30 to enclose the devices 18.

Another integrated circuit package embodiment of the invention, thatincludes dies in a stacked configuration, shown at 300 in FIG. 11,includes thermal interface material at 320 and 340. The integratedcircuit package 300 also includes a substrate 316 electrically coupledto an integrated circuit or die 318 by solder bumps 302 utilized in aprocess commonly referred to as controlled collapsed chip connection(C4). A thermal interface material 340 is used as thermal materialbetween the integrated circuit or die 318 and an integrated heatspreader 322. Some embodiments of the integrated circuit package includea plurality of pins 324 that are attached to a bottom surface 326 of thesubstrate 316.

The integrated circuit or die 318 generates heat that is removed fromthe integrated circuit package 300. The integrated heat spreader 322 isthermally coupled to the integrated circuit 318 to facilitate removal ofheat from the integrated circuit 318. The heat spreader 322 includesmetal and metal alloys that include gold, nickel, and copper, compositematerials, diamond, AlSiC, and other heat conductive materials. In someembodiments, the metal and metal alloys are optionally coated withanother metal or include a thermally conductive composite material.

To decrease the thermal impedance between the integrated circuit 318 andthe heat spreader 322, thermal interface material 340 is placed betweenthe integrated circuit 318 and the heat spreader 322. In one embodiment,the thermal interface material used includes a polymer solder hybridcomposition that includes fusible particles and non-fusible fillerparticles.

The heat spreader 322 includes surfaces 390 and 391 that contact thethermal interface material 320 and 340, respectively. Each of thesurfaces 390 and 391 are patterned with a plated or coated design, suchas is shown in FIGS. 1, 2 and 3 or other preselected design. In oneembodiment, the surfaces 390 and 391 of the heat spreader 322 alsoinclude perturbations, such as channels, serrations, and grooves. Inanother embodiment, the surfaces 390 and 391 of the heat spreaderinclude perturbations but are not plated or coated. In anotherembodiment, one of the heat spreader surfaces 390 is coated or platedwith a pattern such as is shown in FIG. 1, 2, or 3 or other preselecteddesign. The other heat spreader surface 391 includes perturbations,channels or serrations. In another embodiment, the heat spreader surface391 has a different design pattern from the heat spreader surface 390.

The integrated circuit package 300 also includes a thermal element suchas a heat sink, shown at 328, which has a plurality of fins 330. Todecrease the thermal impedance between the integrated circuit 318 andthe thermal element 328, the second thermal interface material 320 isapplied and is placed between the heat spreader 322 and the thermalelement 328. The second thermal interface material 320, for someembodiments, includes the same polymer as the first thermal interfacematerial 340. For other embodiments, the second thermal interfacematerial 320 includes a different polymer from the first thermalinterface material 340.

One other integrated circuit package, illustrated at 400 in FIG. 12,includes a metal substrate 402 and a stiffener 418, overlaying the metalsubstrate. The stiffener 418 is adhered to the metal substrate 402 by anadhesive, which, in one embodiment, is a thermal interface material 419.A die 414 overlays the stiffener 418 and is adhered by an adhesive,which in one embodiment, is a thermal interface material 416. Anintegrated heat spreader 420 overlays the die 414 and the stiffener 418.Thermal interface material adheres the integrated heat spreader 420 tothe die 414 at 422. Thermal interface material adheres the heat spreader420 to the stiffener 418 at 422 and 426.

The integrated heat spreader includes a surface 428 that faces the die414 and surfaces 430 and 432 that face the stiffener. Each of thesurfaces 428, 430 and 432 are patterned with a plated or coated design,such as is shown in FIG. 1, 2 and 3 or other preselected design. In oneembodiment, the surfaces 428, 430 and 432 of the heat spreader 420 alsoinclude perturbations, such as channels, serrations, and grooves. Inanother embodiment, the surfaces 428, 430 and 432 of the heat spreader420 include perturbations but are not plated or coated. In anotherembodiment, one of the heat spreader surfaces 428 is coated or platedwith a pattern such as is shown in FIG. 1, 2, or 3 or other preselecteddesign. The other heat spreaders surface 430 and 432 includesperturbations, channels or serrations. In another embodiment, each ofthe heat spreader surfaces 428, 430 and 432 has a different designpattern from the heat spreader surface 390.

FIG. 13 illustrates a schematic view of a fan 535, including itstangential air flow component 530 and its normal air flow component 532,and a side view of a bent fin heat sink 500 as positioned upon asectioned IC package 550 on a substrate 560, in accordance with oneembodiment of the invention.

The fan 535 is an axial flow fan having a plurality of fan blades 536,rotating in a direction indicated by arrow 538, and disposed about anaxis of rotation 537. The fan 535, when rotating about axis 537,produces an air flow that can be analyzed as having two differentcomponents. A tangential component 530 comprises a plurality of angularvectors 531 generally increasing towards the fan blade periphery. Anaxial component 532 comprises a plurality of downward vectors 533, againgenerally increasing towards the fan blade periphery.

Because the fins 502 of bent fin heat sink 500 are angled towards, orface, the tangential component 530, a relatively greater air flow,represented by arrows 540, is captured and flows downward between fins502, exiting in the direction of arrows 542 beneath bent fin heat sink500.

A thermal plug 523 of bent fin heat sink 500 is in thermal contact withan IC package 550. IC package 550, illustrated in cross-section,includes a die 554 mounted on a package substrate 552 and covered with alid or integrated heat spreader (IHS) 558. The heat spreader includes asurface that is coated or plated to form a design, such as has beendescribed for previous embodiments. A thermal interface material 556 islocated between die 554 and IHS 558. Likewise, a thermal interfacematerial is optionally used, between IHS 558 and thermal plug 523. Someof the relative dimensions of the structures shown in FIG. 14 areexaggerated or diminished, and they are not drawn to scale. For example,in a different embodiment the thermal plug 523 could be as wide as IHS550, with bent fin heat sink 100 accordingly widened to accommodate anIHS 550 of such width.

The heat spreader 550 includes a surface 551 that adheres to the die 554by the thermal interface material 556. The surface 551 is patterned orcoated to form a design as has previously been described herein. Thesurface 551 optionally includes perturbations described herein. Inanother embodiment, the surface 551 includes perturbations but is notcoated or plated to form a preselected design.

The “electronic assembly” is part of an “electronic system.” An“electronic system” is broadly defined herein as any product comprisingan “electronic assembly”. Examples of electronic systems includecomputers (e.g., desktop, laptop, hand-held, server, etc.), wirelesscommunications devices (e.g., cellular phones, cordless phones, pagers,etc.), computer-related peripherals (e.g., printers, scanners, monitors,etc.), entertainment devices (e.g., televisions, radios, stereos, tapeand compact disc players, video cassette recorders, MP3 (Motion PictureExperts Group, Audio Layer 3) players, etc.), and the like.

Thus, since the invention disclosed herein may be embodied in otherspecific forms without departing from the spirit or generalcharacteristics thereof, some of which forms have been indicated, theembodiments described herein are to be considered in all respectsillustrative and not restrictive. The scope of the invention is to beindicated by the appended claims, rather than by the foregoingdescription, and all changes, which come within the meaning and range ofequivalency of the claims, are intended to be embraced therein.

1. A heat dissipating device, comprising: a main body having an outersurface that is plated or coated with at least two different metals,wherein all of the at least two different metals contact a thermalinterface material to form a design effective for bonding to solder andfor adhering to polymer in the thermal interface material, the designcomprising one or more of a circle, a square or a rectangle.
 2. The heatdissipating device of claim 1, wherein the two metals are one or more ofthe combinations of Ni/Au, Ni/Ag, Cu/Au, Cu/Ag, and Cu/Ni.
 3. The heatdissipating device of claim 1 wherein the design is a checkered squaregrid.
 4. The heat dissipating device of claim 1 wherein the design is agrid comprising circles.
 5. The heat dissipating device of claim 1wherein the design is a bull's Eye.
 6. The heat dissipating device ofclaim 1 wherein the design comprises corner squares.
 7. The heatdissipating device of claim 1 wherein the design comprises a centralsquare.
 8. An integrated circuit package comprising the heat dissipatingdevice of claim
 1. 9. An electronic system comprising the integratedcircuit package of claim
 8. 10. An electronic assembly comprising theintegrated circuit package of claim
 8. 11. The heat dissipating deviceof claim 1, further comprising channels or grooves or serrations or oneor more of channels, grooves and serrations defined by the surface. 12.An electronic system, comprising: an electronic assembly comprising aheat dissipating device, comprising: a main body having a surface thatis plated or coated with at least two different metals wherein all ofthe at least two different metals contact a thermal interface materialto form a design effective for bonding to solder and for adhering topolymer in a polymer solder hybrid, the design comprising one or more ofa circle, a square or a rectangle.
 13. The electronic system of claim 12wherein the surface of the main body further comprises perturbations.